The invention concerns a C-arm x-ray device for 3D imaging.
X-ray detectors are used to generate images of a transirradiated subject or body. The x-rays pass through the subject or patient and then strike an image detector on which they form a two-dimensional projection of the transirradiated volume.
Three-dimensional image data can be generated using a plurality of two-dimensional projections of the same x-ray volume. The individual two-dimensional image data are evaluated using a computer to generate a three-dimensional image. For this, the two-dimensional image data must exist digitized, which is why digital image sensors are used and not analog film/foil systems. Digital image sensors directly generate digital, pixelated image data as soon as x-ray radiation is incident upon them. These can be directly fed to a computer for further evaluation.
The generation of three-dimensional image data from two-dimensional x-ray projections assumes that the volume to be reconstructed has in fact been transirradiated in each projection. Stated more precisely, in each individual projection, the central axis of the x-ray beam must pass through a point that it also passes through in all other projections. In order to generate the individual two-dimensional projections, the central x-ray beam thus assumes different orientations in space, whereby a common point of intersection of the central x-ray beam is given for all different orientations. This point of intersection is designated as an isocenter. The specified procedure enables the calculation of a three-dimensional image of a transirradiated volume situated around the isocenter.
In C-arm x-ray devices, the x-ray source and the image sensor are arranged opposite each other on a semicircular (thus C-shaped) carrier. This carrier, the C-arm, can be rotated in the direction of the C-arm circumference in an “orbital direction”, and in a direction perpendicular to this. The patient or subject to be examined is situated substantially in the center of the C-arm, and various orientations of the x-ray beam, and therewith different two-dimensional projections of the transirradiated volume, can be generated via orbital and angular movement.
Two variants differ in C-arm x-ray devices. The first variant comprises an “isocentric C-arm” in which the rotation axis for the orbital motion that runs perpendicular to the plane of the C-arm runs through a point in common with the x-ray beam, namely the isocenter. This ensures that the x-ray beam always runs through the isocenter for each arbitrary orbital orientation, which (as stated above) enables the acquisition of two-dimensional image data that are immediately used to generate three-dimensional images.
The second variant comprises a non-isocentric C-arm in which the central x-ray beam runs through different volumes to be transirradiated for different orbital orientations. The use of the thusly acquired two-dimensional projections for generation of three-dimensional images is at most possible for a limited volume to be reconstructed. For this reason, non-isocentric C-arms exhibit the advantage that they are less expensive to construct and thus are easier and most cost-effective.
U.S. Pat. No. 6,382,835 by the applicant, herein incorporated by reference, discloses a C-arm x-ray device with a non-isocentric C-arm that can generate different orientations of the x-ray beam via angular rotation of the C-arm, and therewith can generate different two-dimensional projections from which a three-dimensional image can be generated. However, the angular motion also allows no large movement range like the orbital motion of the C-arm, which limits the possibilities to generate three-dimensional images.